The invention relates to a novel molding material based on polyisocyanato-isocyanurates and flameproofing and fireproofing agents, as well as optionally polyisocyanates, fillers and promoters, which is particularly suitable for use as construction material and especially from the fire protection standpoint leads to excellent products.
Duroplastic compounds and foams of polyurethane with isocyanate and isocyanurate components, epoxy resins (EPO resins), phenolic resins and novolaks are known, which contain flame-inhibiting additives and which constitute difficulty or nonflammable materials. In order to improve the fire resistance and achieve a low smoke density and toxicity, a large number of different formulations has been proposed. As flame-inhibiting additives are inter alia proposed Al.sub.2 O.sub.3 .times.H.sub.2 O, organic and inorganic phosphates or phosphonates, borates, silicates, chlorinated paraffins, halogen compounds, heavy metal salts, elementary phosphorus, polyphosphates and antimony trioxide. Reference is made in exemplified manner in this connection to U.S. Pats. Nos. 4,126,473 and 4,147,690, European Pat. No. 69 975 and DE-OS 31 05 947. A survey of the prior art appears in Becker-Braun, Kunststoffhandbuch, vol. 7, Polyurethanes, second edition, 1983, Hanser-Verlag; J. Troitzsch, Brandverhalten von Kunststoffen, Grundlagen etc., Carl Hanser-Verlag, 1982; and Polymerwerkstoffe, vol. 2, Technologie 1, H. Batzer et al., George Thieme Verlag, Stuttgart, 1984.
With individual additions or combinations of such flame-inhibiting additives in part very satisfactory results are obtained. In view of the great increase in the use of plastics, nowadays extreme demands regarding fire protection are made in the field of the conveyance of passengers through a number of standards and specifications, particularly with respect to the aircraft and car industry, as well as in ships, trains and in the building industry. This is documented in various national and international test standards, such as DIN 75200, DIN 4102, DV 899/35 (Germany), FAR 25.853, MVSS 25.853 (USA), AFNOR P 92-507 (France), etc. As it is to be expected that these standards will be made even stricter in future and apart from non-flammability, special importance will be attached to the density and toxicity of the smoke gas in the case of charring and/or fires, in 1979 the Airbus consortium drafted its own stricter standards, ATS 1000.001 and made it available to the relevant branches of industry. In the case of an estimated aircraft life of at least 15 years, this standard already takes account of future technical developments and demands (cf. TU 21, 1980, No. 2, February, pp 79-82 and "Die chemische Produktion", 1983, pp 50-53).
The one- and two-component molding materials presently used in the aircraft industry do not yet meet the requirements of ATS 1000.001, as can be gathered from the following table where, for comparison purposes, details are also given of a cured molding material according to the invention. The tests were carried out on sandwich components and honeycomb materials (phenolic resin honeycombs) conventionally used in aircraft construction and which were filled with molding materials and cured.
TABLE 1 __________________________________________________________________________ Comparison of different molding materials according to ATS 1000.001 (+ satisfied, - not satisfied) phenylformaldehyde molding material EPO molding material resin molding material according to invention 2C 1C* 2C 1C __________________________________________________________________________ Smoke density -- -- + + Toxic pyrolysis gases +/- +/- +/- + Compression strength RT + + + + Compression strength 80.degree. C. + + + + Non-flammability +/- +/- + + Density (&lt;0,75) 0,65 0,55 0,70 0,54 Workability in Nome honeycombs +/- +/- +/- + Adhesion to prepregs of: Epoxy resin + + - + Phenolic resin - - + + Polyimide - - - + Shrinkage &lt;0.5% - - - + Extraction force at points of application of force (inserts): RT (requirement 1200 N) - .about.1200 &lt;1000 &gt;2000 70.degree. C. (requirement 1000 N) - &lt;600 &lt;600 &gt;2000 __________________________________________________________________________ *1C: Already compounded twocomponent material which at very low temperatures (-18.degree. C.) is stable over extended periods of time (about 3 months).
In the aircraft industry such molding materials are e.g. used for producing reinforcements and mountings (inserts), internal coverings (e.g. side walls and partitions, as well as roof coverings), floors, insulating and covering plates, as well as molded parts. Particular preference is given to the use of so-called prepreg components (sandwich honeycomb constructions), which are constituted by phenolic resin honeycombs coated with multilayer resin mats (trade name Nomex). The resin mats (prepregs) comprise E-glass fabrics, which are impregnated with resins based on phenol/formaldehyde, unsaturated polyesters, EPO and polyimides. With a view to increasing stability and saving edging profiles, an edge filling mass is often pressed into the honeycombs on the edges of the sandwich components.
A molding material able to satisfy demands in the foreseeable future must cure without shrinkage and lead to a construction material with a low density of approximately 0.2 to 0.8 g/cm.sup.3, which ensures high bending and compression strengths both at ambient temperature and under continuous thermal influences up to 80.degree. or 130.degree. C. To this must be added the demands in connection with fire and/or charring, namely non-flammability, no dripping, insignificant smoke gas emission and substantially non-toxic pyrolysis gas evolution. For special uses (e.g. fire protection walls in the transportation area of aircraft) higher thermal stability would also be necessary, i.e. the material must be able to withstand e.g. a temperature of 1000.degree. to 1200.degree. C. for 10 minutes. With regards to the conventional composite systems in which such molding materials are used, there must be an optimum connection or adhesion with the materials forming the basis of such composite systems, such as polymers, polycondensates or polyaddition compounds (e.g. unsaturated polyesters, EPO resins, phenolic resins, polyimide or polyurethane). It is necessary or at least desirable to also have an optimum connection or adhesion to metals and materials such as glass and carbon fibres.
The formulations and systems known from the prior art, which are described in numerous patent specifications and applications, only partly fulfil certain of the above requirements or combinations of partial ranges thereof.
Thus, European Patent application 157 143 describes fire-inhibiting sealing compounds, which comprise melamines and a number of fillers which, apart from other inadequacies, have densities of 0.7 to 1.0 g/cm.sup.3.
DE-OS 35 19 581 describes ablation coatings of amine-cured EPO and polysulphide resin mixtures with pre-ox-carbon fibres as a reinforcement which, although resistant to high temperatures, have densities well above 1.0 g/cm.sup.3.
DE-OS No. 27 14 006, DE-OS No. 27 13 984 and DE-OS No. 27 40 504 describe molding materials comprising polyisocyanate and hollow spheres. These are cured through access of atmospheric humidity and optionally after addition of water. Preferably, shortly prior to processing phosphoric acid and/or phosphates or their aqueous solutions or alkali silicate solutions are added. The molding materials described in these patent applications only have a relatively low compression strength in the cured state and are only storage-stable in the form of premixes constituted by polyisocyanates and hollow spheres. However, they are not stable as moisture-curing one-component materials and therefore do not have the processing advantages linked with the latter. Tests have revealed that e.g. mixtures of hollow spheres with 2% polyisocyanates do not give stable materials. Materials produced according to the process of claim 2 of DE-OS No. 27 14 006 (plates with a thickness of 5 to 10 mm) were unable to withstand a temperature of 1080.degree. C. for one minute.